On Wed, Apr 30, 2014 at 09:30:55AM +0000, Liu, Chuansheng wrote: > > From: Peter Zijlstra [mailto:pet...@infradead.org] > > Sent: Wednesday, April 30, 2014 4:55 PM > > To: Wang, Xiaoming > > Cc: mi...@redhat.com; linux-kernel@vger.kernel.org; Liu, Chuansheng > > Subject: Re: [PATCH] lib/spinlock_debug: Tweak the loop time to fit > > different > > _delay() > > > > On Wed, Apr 30, 2014 at 06:40:38PM -0400, Wang, Xiaoming wrote: > > > loops_per_jiffy*Hz is not always 1 second exactly > > > it depends on the realization of _delay() . > > > delay_tsc is used as _delay() in arch/x86/lib/delay.c > > > > This just states delay() is broken. The primary response should be to > > try and fix that, no? > > > delay(1s_count) is accurate, but delay(1) is not accurate indeed, since > executing > some instruction, then the 1 cycle delay maybe be used already.
OK, so there's (finally) a problem statement, so is there anything sane we can do about that? But yes, a trylock is a cmpxchg, and a cmpxchg on a contended cacheline can be _much_ longer than one loop. Now the real problem is coming up with something that'll work for all architectures. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
